The present invention relates to a dielectric thin film having a perovskite structure, a method for producing the same and an electronic component made therefrom.
Oxide thin film materials having the perovskite structure have been used in a wide range of applications such as capacitor elements, ferroelectric memory elements and optical sensors owing to their extremely divergent functions including ferroelectric properties, high permitivity, electro-optical effect, piezoelectric effect, pyroelectric effect and superconductivity. For example, one such suitable application is the use as capacitors for DRAM(dynamic random access memory), MMIC(microwave monolithic integrated circuit) and MCM(multi chip module).
Particularly, the development of memory elements noting the high permitivity characteristic and ferroelectric characteristic of perovskite oxide thin films have recently been in the limelight and studies have been made on their use as DRAM capacitors aiming at high level integration due to reduced capacitor areas as well as their use as nonvolatile ferroelectric memories capable of high speed operation by virtue of hysteresis characteristic due to the ferroelectric properties.
However, the oxide thin film materials of the perovskite structure are crystalline materials in contrast to the conventional amorphous-system materials such as SiO2 and Si3N4. As a result, high-level thin film crystal growing techniques and defect control techniques are required in order to realize the manifestation of desired characteristics. For instance, Pb(ZrmTi1-m)O3-system materials are used as nonvolatile ferroelectric memory materials since their spontaneous polarization values are high and Curie temperatures are comparatively high, e.g., over 300xc2x0 C.
In this connection, it has been known that the characteristics are deteriorated markedly due to the formation of cation vacancies due to the volatility of Pb, the formation of oxygen defects in the vicinity of Pt electrode interfaces, the introduction of defects due to such semiconductor process as the formation of passivation films and the like. Particularly, the deterioration of spontaneous polarization due to the polarization reversing cycles or so-called fatigue characteristic is deeply attributable to the above-mentioned defects, thus giving rise to difficult problems in practice. In addition, the Pb-type perovskite has a tendency toward forming a heterogeneous phase having a pyrochlore-type structure which considerably deteriorates ferroelectric properties in the course of thin film low temperature processes, thus also giving rise to a difficult problem in practical use.
On the other hand, BaTiO3 has been well known as a ferroelectric perovskite structure oxide with no Pb and it is extremely stable in structure as compared with the Pb-system perovskite. However, such BaTiO3-system materials are low in spontaneous polarization and their Curie point is 120xc2x0 C. which is close to room temperature. As a result, the temperature dependency of the polarization amount is extremely large so that these materials have been considered unsuitable for use as nonvolatile capacitors for ferroelectric memory elements.
In view of the foregoing deficiencies, it is an object of the present invention to provide a dielectric thin film which is stable thermodynamically, capable of effectively utilizing the lattice strain due to lattice mismatch and further capable of realizing reduced leakage current and improved fatigue characteristic, a method of producing the same and an electronic component made therefrom.
[Means of Solving the Problem]
To accomplish the above object, the present invention is characterized in that {X1} having a 12-oxygen atom coordination structure and {X3} which is different in coordination structure from the {X1} are each constituted by at least one element selected from the group consisting of Ca, Mg, Sr, Ba and Pb, that {X2} having a 6-oxygen atom coordination structure is constituted by at least one element selected from the group consisting of Ti and Zr, and that ┌O┘ represents oxygen, whereby {X3}O is inserted between perovskite layers having a composition of {X1}{X2}O3 and formed on a substrate of the similar crystallographic structure thereby forming a lattice strain due to the lattice mismatch between the substrate and the layered perovskite film interleaved with {X3}O.
Another invention is characterized in that it consists in a dielectric thin film having a composition of {X}m{X2}O2+m (where m greater than 1) wherein {X1} having a 12-oxygen atom coordination structure and {X3} which is different in coordination structure from {X1} are each constituted by at least one element selected from the group consisting of Ca, Mg, Sr, Ba and Pb, and {X2} having a 6-oxygen atom coordination structure is constituted by at least one element selected from the group consisting of Ti and Zr, with {X} representing the total sum of the constituting elements of the {X1} and {X3} and ┌O┘ representing oxygen, and the dielectric thin film includes a plurality of perovskite layers having a composition of {X1}{X2}O3 and formed on a substrate similar in crystallographic structure thereto and {X3}O inserted between the perovskite layers, thus causing a lattice strain due to the lattice mismatch between the substrate and the film.
Still another invention is characterized in that {X1} having a 12-oxygen atom coordination structure and {X3} which is different in coordination structure from the {X1} are each constituted by at least one element selected from the group consisting of Ca, Mg, Sr, Ba and Pb, that {X2} having a 6-oxygen atom coordination structure is constituted by at least one element selected from the group consisting of Ti and Zr and that ┌O┘ represents oxygen, whereby {X3}O is two-dimensionally or three-dimensionally inserted between perovskite layers having a composition of {X1}{X2}O3.
The above and other objects, features and advantages of the present invention will become apparent from the following detailed description taken with the accompanying drawings.